Diamond has proven to be useful in a wide variety of applications. For example, cutting elements used in earth-boring tools often include a polycrystalline diamond (PCD) material, which may be used to form polycrystalline diamond compact cutting elements (often referred to as “PDCs”). Such polycrystalline diamond cutting elements are conventionally formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (e.g., cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) comprising a plurality of particles of hard material in a metal matrix, such as, for example, cobalt-cemented tungsten carbide. In such instances, catalyst material in the cutting element substrate may be drawn into the diamond grains or crystals during sintering and catalyze formation of a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process.
Earth-boring tools for forming wellbores in subterranean earth formations that may include a plurality of cutting elements secured to a body include, for example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”). Such fixed-cutter bits include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit, conventionally in pockets formed in blades and other exterior portions of the bit body. Other earth-boring tools may include rolling cone earth-boring drill bits, which include a plurality of cones attached to bearing pins on legs depending from a bit body. The cones may include cutting elements (sometimes called “teeth”) milled or otherwise formed on the cones, which may include hardfacing on the outer surfaces of the cutting elements, or the cones may include cutting elements (sometimes called “inserts”) attached to the cones, conventionally in pockets formed in the cones. Cutting elements that include diamond increase the useful life of the earth-boring tools to which they are attached because the diamond increases the strength and abrasion resistance of the tools. Still other earth-boring tools incorporate diamond that may not be polycrystalline diamond. For example, impregnated earth-boring drill bits generally comprise a plurality of diamond particles, which may comprise polycrystalline diamond or may simply comprise monocrystalline diamond, embedded in a matrix material.
Diamonds also have desirable properties that render them useful in still other applications. For example, the high strength and abrasion resistance of diamonds renders them useful in grinding, polishing, and machining applications. In addition, diamonds are commonly used as additives to coatings that may be applied, for example, to abrasive articles or other structures. Increased thermal conductivity of diamonds renders them useful as particles dispersed in lubricants, such as motor and pump oils, because such lubricants often serve to cool the parts they lubricate. Furthermore, increased electrical conductivity of some diamonds (e.g., blue diamonds and synthetic diamonds formed by chemical vapor deposition act as semiconductors, though most diamonds act as dielectrics) renders them useful as fillers in polymers and elastomers, where increased electrical conductivity in at least some portion of the polymers and elastomers is desirable.
During use, during processing, or both, diamond particles may be dispersed in a fluid or gel continuous phase material to form a paste or slurry. For example, a suspension comprising dispersed diamond particles may be employed to deposit a uniform quantity of the diamond particles in a mold for subsequent processing into a PDC cutting element. It is known, however, that dispersed diamond particles may tend to agglomerate and sediment due to their relative instability in common continuous phase materials, such as water and alcohol.
Some attempts have been made to enhance the stability of diamond particles in suspensions. For example, U.S. Pat. No. 6,337,060, issued Jan. 8, 2002, to Hiraki et al. discloses, among other things, that diamond particles of 2 μm or less may be rendered hydrophilic by boiling in a concentrated sulfuric acid solution at a temperature greater than 200° C. Likewise, U.S. Pat. No. 6,372,002, issued Apr. 16, 2002, to D'Evelyn et al. discloses, among other things, that functionalized diamond may be produced by boiling diamonds in a strongly oxidizing acid, which may produce carboxyl groups (—COOH) on the diamond surface to render it hydrophilic. U.S. Provisional Application No. 61/324,142, filed Apr. 14, 2010 and entitled “Method of Preparing Polycrystalline Diamond from Derivatized Nanodiamond,” discloses, among other things, that nanodiamonds may be derivatized to include functional groups on the surface thereof and then mixed with microscale diamonds, which mixture is then used to form a polycrystalline diamond material.